Mosquito season in Washington County, MO: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, MO starts around March 31 and ends around November 1, about 31 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by March 17.
- Book any yard treatment for late March, ahead of the July peak.
- Repellent can go away after November 1.
- No West Nile cases since 2016, so bites in Washington County are a nuisance; check window screens.
Washington County against the rest of MO
Washington County has the 43rd longest season of 115 MO counties, at 215 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 54.7°F.
- McDonald County: March 31 to November 1 (215 days, 0 WNV)
- Osage County: March 31 to November 1 (215 days, 0 WNV)
- Webster County: April 1 to November 2 (215 days, 1 WNV)
- Bollinger County: April 1 to November 1 (214 days, 0 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Washington County (1 neuroinvasive) across 1 year. The worst was 2002 with 1; the latest was 2002.
See how the dates are worked out, and when mosquitoes go away for the winter.